DTI-MRI Reveals Long-Term Effect of Blast-Induced Brain Injuries

Using a form of magnetic resonance imaging (MRI), researchers revealed that soldiers who suffered mild traumatic brain injury (MTBI) triggered by blasts exhibit long-term brain differences.

The findings were presented December 2, 2013, at the annual meeting of the Radiological Society of North America (RSNA), held in Chicago (IL, USA). Recent conflicts have resulted in veterans with an exposure rate of about 20% to blast-induced MTBI or trauma resulting from mortar fire and improvised explosive devices. Diagnosis can be challenging, especially in mild cases. “Mild traumatic brain injury is difficult to identify using standard CT [computed tomography] or MRI,” said study coauthor P. Tyler Roskos, PhD, a neuropsychologist and assistant research professor at the Saint Louis University School of Medicine (St. Louis, MO, USA). “Other methods may have added sensitivity.”

One of these methods is diffusion tensor imaging (DTI), an MRI application used to identify microstructural injury to white matter, the region of the brain that consists mostly of signal-carrying axons. Damage-associated alterations in water movement along the axons are comparable in specific aspects in respect to what might occur with a garden hose, according to co-author Thomas M. Malone, BA, research associate at Saint Louis University School of Medicine. “As water passes through the hose from the faucet to the sprinkler, it goes in the same direction, but if you were to puncture the hose with a rake, the water would shoot out the sides,” Mr. Malone said.

In the study, researchers compared DTI-derived fractional anisotropy (FA) values in 10 veterans of US Military Operations Iraqi Freedom and Enduring Freedom who had been diagnosed with MTBI with those of 10 healthy control subjects. FA gauges the uniformity of water diffusion throughout the brain, and low FA tends to indicate areas of axonal injury. The median time elapsed between the blast-induced injury and DTI among the patients was 51.3 months. “The time since injury is a novel component to our study,” Dr. Roskos said. “Most other blast-related MTBI studies examine patients in the acute phase of injury.”

Comparison of FA values showed considerable differences between the two groups, and there were significant correlations between FA values and attention, delayed memory, and psychomotor test scores. Because the victims were mostly more than four years removed from their injuries, the findings indicate the presence of a long-term impact of blast injury on the brain. “This long-term impact on the brain may account for ongoing cognitive and behavioral symptoms in some veterans with a history of blast-related MTBI,” Dr. Roskos said.

The findings also suggest that DTI is sensitive to group differences in blast-related MTBI even in the post-acute phase. “DTI shows promise in enhanced sensitivity for detecting MTBI compared to MRI/CT, even in the chronic phase,” Dr. Roskos said. “Identification of changes in specific brain regions may help in diagnosis and treatment of MTBI among veterans.”

Dr. Roskos explained that this research is geared at searching for better ways for the clinician to differentiate between MTBI and post-traumatic stress disorder (PTSD) in veterans to optimize treatment. “It makes a difference, because PTSD is psychological in nature and MTBI is neurological,” he said. “Many veterans in the healthcare system are dealing with MTBI, PTSD, or both. Our emphasis today is to find the best treatments and measure the patient’s progress. Imaging has the potential to do that.”

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Saint Louis University School of Medicine